How can I get adc value in main statement?

[lee_daeun]

I am using 5 adc values (emg[5]) and can get the value of them.

I want to use these values in the main statement, so I assigned it.

However I can't get the value. It's always zero.  (good[0] = emg[0])

Can I know what's the matter of this,,? Thanks for help!

[waclawek.jan]

HAL_ADC_Start_DMA() is asynchronous, it means, that it starts the hardware process with ADC and DMA and returns immediately, not waiting for the result. It takes time until the hardware - ADC and DMA - performs the conversions, so you can't read out the results immediately after that function was called.

DMA signals when it's finished by the Transfer Complete interrupt, the is a callback in Cube/HAL which is called at that point and may be a good point to read the results. I don't use Cube/HAL, refer to is documentation or to the examples.

JW

[TDK]

If you want to use polling mode, see here for an example:

STM32CubeF4/Projects/STM32F413ZH-Nucleo/Examples/ADC/ADC_RegularConversion_Polling/Src/main.c at 82738194a5e85ee5331975b04905daa0a17053ec · STMicroelectronics/STM32CubeF4 (github.com)

If you want to use DMA, see here for an example:

STM32CubeF4/Projects/STM32F446ZE-Nucleo/Examples/ADC/ADC_RegularConversion_DMA/Src/main.c at 82738194a5e85ee5331975b04905daa0a17053ec · STMicroelectronics/STM32CubeF4 (github.com)

Conversions are not complete until HAL_ADC_ConvCpltCallback is called from an interrupt.

[Andrew Neil]

Please see the Posting Tips for how to properly post source code - not as screenshots:

https://community.st.com/t5/community-guidelines/how-to-write-your-question-to-maximize-your-chances-to-find-a/ta-p/575228

[SofLit · Accepted solution]

Hello @lee_daeun and welcome to the community,

First, as stated by @Andrew Neil , you need to copy paste your code using the button </> instead of posting the screenshots.

Second, as stated by @waclawek.jan ,

The DMA transfer is not starting immediately after calling HAL_ADC_Start_DMA():

HAL_ADC_Start_DMA(&hadc1, (uint32_t*) emg, 5);
good[0] = emg[0];

So you need to use interrupt callback HAL_ADC_ConvCpltCallback() and read emg ADC buffer there.

[Andrew Neil]

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@SofLit wrote:

The DMA transfer is not starting immediately after calling HAL_ADC_Start_DMA():.

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It should be starting, but it won't have finished - therefore the results are not yet available.

[SofLit]

Indeed, I didn't express myself well ..

[lee_daeun]

Thanks a lot! I got an answer